Poly-2-pyrrolidone, which is also known as nylon-4, is believed to be a linear polymer characterized by the repeating structural unit ##STR1##
The polymer is capable of being formed into filaments having substantial orientation along the filamentary axis, high tensile strength, and other properties suitable for making into textiles. The polymer is also suitable for making into films, sheets, shaped and molded articles. Poly-2-pyrrclidone is formed by the alkaline catalyzed polymerization of 2-pyrrolidone.
The present invention relates to an improved process for the polymerization of 2-pyrrolidone. Methods for the alkaline-catalyzed polymerization of 2-pyrrolidone have been previously described, for example, in U.S. Pat. Nos. 3,721,652, 3,174,951, 3,681,296, 3,681,295 and 2,638,463. In general, these methods effect polymerization in the presence of a polymerization activator (initiator) as well as the alkaline catalyst. Sulfur dioxide has been found to function as a polymerization activator for the polymerization of 2-pyrrolidone, see U.S. Pat. No. 3,174,951, but the SO.sub.2 -initiated polymer product has a distinct yellow color which is highly undesirable, see U.S. Pat. No. 3,681,295. Carbon dioxide also functions as a polymerization activator for the alkaline catalyzed polymerizaton of 2-pyrrolidone, see U.S. Pat. No. 3,721,652.